The invention relates to a method for maintaining freshness of a cut flower by which the life of the cut flower can be considerably prolonged.
Recently, cut flowers are widely used for ornamental use. As a result of that, it is demanded to maintain the freshness of the cut flower for a prolonged time. Various methods for maintaining the freshness of cut flower have been proposed. For example, a method of frequently changing water, a method of cutting the stem of flower in water and a method of burning the cut end of the flower, have been known. Furthermore, a method has been known in which the cut end of the flower is immersed in a solution containing a certain chemical. As the solution for the immersing, a solution of 8-hydroxyquinoline, a solution of sucrose, a solution of silver nitrate and a solution containing a silver thiosulfate complex are known.
However these methods are not always sufficient. In some cases, the methods are ineffective depending on the kind of the flower. For example, J. Am. Soc. Hort. Soci., 102, p. 76, 1977, reports that the moving speed of silver nitrate in the trachea of a plant is very slow and the effect of which is not clear. The silver-thiosulfate complex is ineffective to a flower having a low sensitivity to ethylene such as rose and chrysanthemum, even though the complex is effective to a flower having a high sensitivity for ethylene such as carnation, sweet pea and babies-breath. With respect to a cut flower of rose, a mixture and/or reaction product of a silver compound and an amino acid has been disclosed in Japanese Patent Publication Open for Public Inspection, hereinafter referred to JP O.P.I., No. 06-321701, and a mixture or a reaction product of a silver compound and a primary amine and/or a substance relating to nucleic acid has been disclosed in WO 93/08685. However, these compounds are insufficient in the effect thereof.
The object of the invention is to provide a method for maintaining the freshness of a cut flower by which the life of the flower can be considerably prolonged.
The objects of the invention are attained by a method for maintaining the freshness of a flower comprising the step of making imbibe an aqueous solution of a composition for maintaining the freshness of flower which comprises a mixture or a reaction product of a silver compound and an organic compound having a functional group capable of forming a water-soluble complex with a silver ion through the sulfur atom thereof to a flowering plant.
As the functional group capable of forming a water-soluble complex with a silver ion through the sulfur atom thereof, the following are cited:
xe2x95x90Cxe2x95x90S, xe2x95x90Sxe2x95x90S, xe2x95x90S(xe2x95x90S)xe2x95x90, xe2x95x90P(xe2x95x90S)xe2x80x94 and xe2x80x94Sxe2x80x94.
Examples of the organic compound of the invention having a functional group capable of forming a water-soluble complex with a silver ion through the sulfur atom are those represented by the following Formula 1, 2, 3, 4 or 5. 
wherein R1 and R2 are each a monovalent group which are each bonded with the carbon atom through a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, provided that at least one of R1 and R2 is an organic group, 
wherein R3 and R4 are each a monovalent group which are each bonded with the sulfur atom through a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, provided that at least one of R3 and R4 is an organic group, 
wherein R5 and R6 are each a monovalent group which are each bonded with the sulfur atom through a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, provided that at least one of R1 and R2 is an organic group, and X is an oxygen atom or a sulfur atom. 
wherein R7, R8 and R9 are each a monovalent group which are each bonded with the phosphor atom through a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, provided that at least one of R7, R8 and R9 is an organic group,
R10xe2x80x94Sxe2x80x94R11xe2x80x83xe2x80x83Formula 5
wherein R10 and R11 are each a monovalent organic group.
In the foregoing Formulas 1 to 4, xe2x80x9cthrough a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atomxe2x80x9d means the group represented by R1, R2, R3, R4, R5, R6, R7, R8, or R9 each has a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom and the group is bonded through this atom with the carbon atom, sulfur atom or the phosphorous atom of Formula 1, 2, 3, or 4.
The xe2x95x90Cxe2x95x90S group capable of forming a water-soluble complex with a silver ion through the sulfur atom includes, for example, a thiocarbonyl group, a thioacyl group, a thioamido group, a thioaldehyde group, a thioureido group, a thioureine group and an isothiocyanato group.
Examples of the organic compound having the xe2x95x90Cxe2x95x90S group, a thioketone group, a thioaldehyde group, an O-carbothio acid and its ester, a thiourea derivative, a thioamide, a thioimide, and an isothiocyanate.
The foregoing thiourea derivative includes, for example, thiourea, N-methylthiourea, allyl-2-thiourea, 2-imidazolinethione, 1-allyl-3-xcex2-hydroxylethyl-2-thiourea and 2-thiobarbituric acid.
As the compound having isothiocyanate, for example, ethyl isothiocyanate is cited.
As the organic compound having the xe2x95x90Sxe2x95x90S group capable of forming a water-soluble complex with a silver ion through the sulfur atom, For example, a thiosulfinic acid derivative and its ester, and a thiosulfinamide are cited. In concrete, p-toluenethiosulfinamide is cited.
As the organic compound having xe2x95x90the S(xe2x95x90X)xe2x95x90S group capable of forming a water-soluble complex with a silver ion through the sulfur atom, for example, a thiosulfonic acid derivative and its ester are cited. In concrete, potassium p-toluenethiosulfonate and dimethylthiosulfuramide are cited.
As the organic compound having the xe2x95x90P(xe2x95x90S)xe2x80x94 group capable of forming a water-soluble complex with a silver ion through the sulfur atom, for example, a thiophosphonic acid derivative and its ester and a thiophosphoric acid ester are cited. In concrete, for example, disodium methanethiophosphonate and dimethylthiophosphoramide are cited.
Examples of the compound represented by R10xe2x80x94Sxe2x80x94R11, which is a compound having the xe2x80x94Sxe2x80x94 group capable of forming a water-soluble complex with a silver ion through the sulfur atom, include an organic sulfide, an S-ester of thiocarboxylic acid such as S-ester of carbothioacid, an ester of carbodithioacid, an S-ester of thiocarbonic acid such as S-ester of thiocarbonic acid, an S-ester of dithiocarbonic acid and an ester of trithiocarbonic acid.
As the foregoing organic sulfide compound, for example, a dithio compound such as 2,2xe2x80x2-thioglycolic acid, 2,2xe2x80x2-thiodiethanol, 3,3xe2x80x2-thiodipropionic acid, a polyalkylene thioglycol such as 3,6-dithia-1,8-octanediol are cited.
As example of ester of thiocarboxylic acid, S-methyl ester of 1-dihydroxyethyl-2carboxylic thio acid is cited.
As the silver compound in the invention, a monovalent silver compound is useful, and a silver salt is preferred. Example of the silver salt includes silver nitrate, silver carbonate, silver acetate, silver sulfate, silver chloride, and silver bromide.
The formation of water-soluble complex of the organic compound having a sulfur atom with a silver ion can be confirmed by measuring the silver electrode potential of the solution. When the complex is formed, the free silver ion concentration in the solution is lowered by the addition of the organic compound. The lowering of the silver ion concentration can be confirmed by lowering of the potential between the silver electrode and a reference electrode each immersed in the solution.
The composition of the invention for maintaining the freshness of cut flower can be prepared by mixing the silver compound and the organic compound having the functional group capable of forming a water-soluble complex or salt with a silver ion. The form of the composition of the invention for maintaining the freshness of cut flower is not specifically limited, and the composition may be in a form of solution, solid and powder. The form of an aqueous solution is most preferable.
The composition of the invention for maintaining the freshness of cut flower is preferably prepared by mixing an aqueous solution of the silver compound and an aqueous solution of the organic compound having the functional group capable of forming a water-soluble complex or salt with a silver ion.
The concentration of silver in the composition of the invention for maintaining the freshness of cut flower is from 0.001 millimoles/liter to 5 millimoles/liter, preferably from 0.005 millimoles/liter to 1 millimoles/liter, even though the concentration is not specifically limited. The molar ratio of silver to the organic compound having the functional group capable of forming a water soluble complex with a silver ion is preferably from 1/100 to 1,000, particularly preferably from 1 to 10.
It is preferred that the composition for maintaining the freshness of cut flower to be used in the invention is further contains a polycation compound or a surfactant.
The polyamine compound is a polymer having a constituting unit which has an amino group capable of forming a quaternary salt. A polyalkylimine is preferably usable as the polycation compound. For example, diethylenetriamine and triethylenetetramine, which are an oligomer of ethyleneimine, and a polyethyleneimine having a larger molecular weight are cited. The molecular weight of such the compound is preferably not more than 1000 even though the molecular weight is not specifically limited.
The concentration of the polycation in the freshness maintaining composition of the invention at the time of use is within the range of from 0.1 to 10, more preferably from 0.3 to 3, in the molar ratio of the cation unit and silver.
As the surfactant relating to the invention, any of a nonionic surfactant, a cationic surfactant and an anionic surfactant are usable, and the nonionic surfactant and the anionic surfactant are preferable. Concrete examples of the nonionic surfactant include a polyoxyethylene ether such as polyoxyethylene (10) octylphenyl ether which is available on the market under the trade name of TRITON X-100 manufactured by Kanto Kagaku Co., Ltd., polyoxyethylene cetyl ether and polyoxyethyele octyl ether, a polyoxyethylenesorbitan ether such as polyoxyethylenesorbitan monolaurate which is available on the market under the trade name of TWEEN-20 manufactured by Kanto Kagaku Co., Ltd., polyoxyethylenesorbitan monooleate, polyoxyethylenesorbitan monopalmitate, polyoxyethylenesorbitan monostearate and polyoxyethylenesorbitan trioleate, one having a cholic acid nucleus such a N,N-bis(3-D-gluconamido-propyl) cholamide, N,N-bis(3-D-gluconamidopropyl) dexycholamide and 3-(3-Cholamidopropyl)-(dimethylammonio)-2-hydroxyopropane-sulfonic acid, one having a sugar chain such as n-dodecyl-xcex2-D-maltopyranoside, n-octyl-xcex2-D-glucopyranoside, n-heptyl-xcex2-D-thioglucopyranoside, n-octyl-xcex2-D-thioglucopyranoside, sucrose monocaprate and sucrose monolaurate, and an alkane amide such as n-octyl-N-methylglucamide, n-nonanoyl-N-methylglucamide and n-decanoyl-N-methylglucamide. Examples of anionic surfactants include sodium dodecylsulfate (SDS), Sodium deoxycholic acid (DOC). TWEEN-20 and SDS are particularly preferable.
The concentration of the surfactant in the using of the freshness maintaining composition is within the range of from 0.00001% to 0.1%, preferably from 0.0001% to 0.05%, particularly preferably from 0.0005% to 0.005%, by weight in gram by volume in milliliter, hereinafter referred to W/V-%.
The composition of the invention is preferably has a pH of from 3 to 11. The composition of the invention for maintaining the freshness of cut flower may contains a buffering agent, an acid or an alkali to control the pH if it is necessary.
A sugar such as sucrose and glucose, an antibacterial agent such as 8-hydroxyquinoline, and a surfactant may be added as a additive according to necessity. A preservant such as a sulfite salt may also be added.
To imbibe the freshness maintaining composition according to the invention to the flower plant, the root of the flowering plant before cutting the flower or the cut end of a cut flower is immersed in an aqueous solution of the solution of the freshness maintaining composition. Thus the life of the cut flower can be prolonged.
Although there is no limitation on the time and the temperature of the immersion, it is preferred to immerse for 1 to 12 hours at a room temperature of from 20 to 25xc2x0 C., and for 4 to 48 hours at a cold storage condition of from 2 to 10xc2x0 C., when the composition is used for a pretreatment.
The freshness maintaining composition according to the invention may be used for a pretreatment, which has also a purpose of water raising, to be applied after picking up of the flower prior to the shipment. The freshness maintaining composition may also be used for a post-treatment of the flower to be applied in the distribution facilities such as a market and a flower shop or at a consumer.
Although there is no limitation on the flower to which the freshness maintaining composition to be applied, the composition is effective to, for example, rose, chrysanthemum, carnation, bouvardia, gerbera, babies-breath, and sweet pea. The composition is particularly effective to rose.